What types of metal pieces can be produced by Investment Casting?

/ / Published in Investment Casting
Defense Piece

The evolution of Investment Casting over the last few years has been directed towards the manufacture of larger and more complex parts, mainly as a way of adapting to the development and innovation of MIM and Additive Manufacturing technology.
These two technologies have eventually been implemented in the manufacture of the smallest range of parts. In the following article, we will explain the evolution of the parts since the beginning of the company, when each technology is best applied, the basic rules and tips to keep in mind when manufacturing or ordering metal parts produced with Investment Casting.

From the experience of more than 50 years of Ecrimesa Group in the manufacture of metal parts, we can see in the image (Figure 1) how has been the evolution of the manufacture of parts with Investment Casting, from smaller parts in 1970 to larger formats in 2010 (Source: Ecrimesa).

Piezas metálicas distintas décadas
Figure 1: Pieces corresponding to the years 1970, 1990 and 2010
(Source: Ecrimesa Sampler)

Even so, size parts are still being manufactured in Investment Casting. We consider small parts as those that are less than 100 grams in weight and remain in the Investment Casting technology due to some technical or economic reasons:

  • Better mechanical properties than other technologies (e.g. safety parts)
  • Steels not developed in other technologies
  • Lower manufacturing cost of the permanent mold for short production runs
  • Rapid prototyping (Figure 3)
  • If no flat surfaces are available for support (MIM parts need it) 
Piezas pequeñas MIM
Figure 2: Examples of small parts that remain in the MF technology
(Source: Ecrimesa)
Impresion tridimensional
Figure 3: 3D printing, no need for permanent molds
(Source: Ecrimesa)

In the following image (Figure 4), we can see graphically which technology is the most suitable according to the complexity/size ratio. MIM, Investment Casting, machining, sand casting or powder metallurgy. In Ecrimesa Group we use metal injection molding, Investment Casting, machining and additive manufacturing, because they are the most efficient technologies and provide us with the best results to meet the technical demands of our customers.

Diagrama comparativo tecnologías
Figure 4: Location of technologies according to batch size and part complexity  
(Source: Ecrimesa)

Any part can be manufactured using Investment Casting technology, with diverse applications: 

  • Carbon construction steels (C45), such as spring steels (50CrV4), quench steels (42CrMo4) or case hardening steels (16MnCr5).
  • Tool steels for cold cutting work (1.2363), quench and tempering steels (1.2343), high-speed steels (1.3343).
  • Ferritic and martensitic stainless steels with easy machining (X12CrMoS17), precipitation steels (174PH), austenitic (1.4408), duplex (1.4582), refractory and valve steels (1.4841).
  • Aluminium.

Ecrimesa Group is specialized in offering customized steels for each type of application. For the manufacture of parts with Investment Casting technology, some basic rules must be taken into account in relation to the production means, dimensional tolerances, design rules and surface finish. Let’s see each one of them: 

Means of production in Investment Casting

  1. The productive means will mark the feasibility of manufacturing a given part. It should be taken into account that these productive means can be greater and although at the beginning they can suppose a restriction, with new productive means they would be solved. 
  • Injection molding: A part mold that requires dimensions larger than the plate opening of the injection molding machine cannot be manufactured (Figure 5).
Inyectora Arburg
Figure 5: Arburg injector, bar spacing up to 520 mm. MPI injector, plate opening 550 mm.
(Source: Ecrimesa)
  • Coatings: Dimensional limitations on the size of slip tanks, sandblasters, fluidized beds and conveyor have to be assessed on feasibility. 
Lecho fluidizado y tanque de barbotina
Figure 6: Fluidized bed and slurry tank
(Source: Ecrimesa automatic coating line)
  • Casting: Dimensional limitation by the gate of the preheating muffle of ceramic molds. 
Puerta de la mufla
Figure 7: Ceramic mold preheating muffle door
(Source: Mufla Ecrimesa)

At Ecrimesa, we currently cast parts in the range of 1 gram to 20 kg. This, depending on the arrangement of the part in its assembly and considering the machining allowances in case it is needed, is equivalent to handling equivalent weights of steel that move between 10 and 50 kg for bunches of parts. In turn, Ecrimesa manufactures parts with special dimensions. The current limitation is defined by a 300 mm cube, being able to be in a dimension up to 650 mm (figure 8) being flat.

Pieza defensa
Figure 8: Example of a 500 mm fender piece
(Source: Ecrimesa)

Dimensional tolerances in the Investment Casting process

  1. MF linear and coaxial dimensional tolerances according to VDG P690 2010.
Tolerancias dimensionales
Table 1: Dimensional tolerances
(Source: Ecrimesa)

The purchase order shall specify the degree of precision of the same. Accuracy D3-A3 will require additional operations to meet them, such as machining. General tolerances are D2 versus D1 of MF low cost.

Design rules in the Investment Casting technique

  1. Design Rules
    As a general rule, the minimum manufacturing thicknesses shall be 2 mm in steel and 1.5 mm in aluminum. Angles and sharp edges shall be avoided (figure 8).
Creces pulido
Figure 8: Crezes to be polished with sharp-edge requirement
(Source: Ecrimesa)
  • Avoid large flat surfaces (add drains and suspenders).
Superficie Plana
Figure 9: 250 mm flat surface with ties
(Source: Ecrimesa)
  • Avoid undercuts (ceramic or soluble wax cores will be required).
Macho cera soluble
Figure 10: Soluble wax core
(Source: Ecrimesa)
  • Avoid abrupt changes of section, design tie rods, bridges to avoid deformations, avoid deep blind holes:
Medidas Longitud Vaciados
Table 2: Casting length measurements as a function of diameter
(Source: Ecrimesa) 
  • Figure 11 shows various practical recommendations for design.
Recomendaciones Diseño
Figure 11: Design recommendations
(Source: Ecrimesa)

Surface finishing in manufacturing with the Investment Casting technique

  1. Surface finish: Figure 10 shows the surface qualities depending on the finish of the part.
Calidades Superficiales
Table 3: Surface qualities
(Source Ecrimesa)
Pieza Mecanizada
Figure 10: Machined part
(Source: Ecrimesa)
Piezas Mecanizadas, Bruñidas y Granilladas
Figure 11: From left to right, Honed part, shot blasted and machined part and honed and machined part.
(Source: Ecrimesa)

For more information about the Investment Casting process in Ecrimesa Group, visit our section:

INVESTMENT CASTING AT ECRIMESA GROUP

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